Parabolic reflector antennas are widely used for line of sight communication in various frequency bands, such as the Ku and Ka bands. The line of sight (LOS) communication may form part of terrestrial point-to-point communication links, or transmission via communication satellites. It is desirable that a feedhorn should be capable of simultaneously illuminating a parabolic reflector at two frequencies, e.g. the Ku and Ka bands. The antenna beams produced at both frequency bands should be centered along the same boresight axis. This requires the use of a multi-band feed. It should be noted that the term “illuminating” refers to reception and/or transmission of signals.
WO 01/91226 describes a dual-band feed having two circular waveguides mounted coaxially with one another. A high frequency waveguide is mounted coaxially within a lower frequency waveguide. An arrangement of turnstile junctions and connecting waveguides joins the coaxial waveguides to other apparatus.